"A DC-8-40 became the first jet airliner to exceed the speed of sound when, in 1961, it reached Mach 1.012 (667 mph) in a shallow dive"
- The Flier's Handbook, Pan Books, 1978.

Are modern airliners of the Airbus, Boeing or McDonnell Douglas variety able to perform the above without structural damage (at least for short periods)? I understand that the slim DC-8 fuselage did not give as much drag as today's "fat jets".

I would say yes, 'normal' airliners can exceed Mach 1.0 for short periods of time (and are tested under those conditions). In almost all cases, that could only really happen in a dive. But in the event that a plane was diving, for whatever reason, you certainly wouldn't want it to reach M1 and start breaking up.

As MITaero said, someone should be able to provide a more conclusive answer.

They shouldn't but there's an ex-TWA 727 and an ex-Evergreen 747 that have both done rolls and supersonic excursions. the 727 was pretty beat up as the gear had to be lowered to get things back to reality but the 747 had 1.084 Mach on the FDR and not much but the seat cushions were hurt.

One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533

Not really. I'm pretty sure and have heard (here at Boeing) that they are tested at above Mach 1. What happens if an aircraft enters a dive for some (horrible) reason? Should it break up, or should the pilots have a chance to recover?

Tested? Not to my knowledge. Why would you test a subsonic airliner at transonic or supersonic speeds? Just for kicks?

Like MITaero said, what happens if the airliner in question ever enters a dive?! After all, there's a decent chance that that could happen somewhere along the line... You need to know how the aircraft will behave in that situation, so testing is a very reasonable thing to do.

This is akin to testing an automobile at the bottom of the ocean.

Not really. If you drive your car into the ocean, you drown - who cares how the car behaves? Enter a dive in an airliner and reach M1, and you're still alive and well (worrying whether the plane will break up or not, no doubt).

Agree with Airplay. Subsonic airliners are certainly not designed to go supersonic, neither is that a part of the test program.

But any jet airliner would aerodynamically be able to break the sound barrier in a dive. Whether they break up doing so, or to what degree they get damaged, or if they suffer damage at all, that will depend very much upon the altitude. Also at supersonic speed is thin air a lot less violent than thick air.

Most airliners will already in the transonic region suffer from ineffective controls, especially ailerons and elevator. Also they are not designed to shift center of gravity like the Concorde was.

Some airliners will be able to compensate for ineffective elevator control using the tailplane trim, much the same way as Chuck Yeager did on the Bell X-1 in 1947. But that will of course only help if the tailplane doesn't separate.

Supersonic flight is not just "going faster". It is flying in accordance with entirely different physical laws. Subsonic airliners are optimized for what they are designed for and do not take supersonic laws into account.

Always keep your number of landings equal to your number of take-offs, Preben Norholm

No one is arguing that subsonic aircraft are not designed for subsonic conditions. Further, Qantas and I are familiar with the physics of supersonic flows. Although a plane will perform horribly for M>1, it will not be an uncontrollable brick. How did the DC-8 mentioned in the first post pull out of its dive?

I do know that Boeing performs many off-design flight tests, and I believe overspeed testing is part of these. (Overspeed as in Mach number, not just "going faster".)

There have been a few cases of airliners going wupersonic in regular pax service- unfortunately the end result was the destruction of the a/c and the loss of all on board. A few that come to mind: Silk Air 737, Egypt Air 767,PSA BA146. In all these cases the plane was in a supersonic nosedive and brokeup around the 10,000 feet mark.

the citation x test pilots have had to break it when flying that plane. i mean, it soo close...

The Citation X was indeed flown slightly past Mach 1 by the Cessna test pilots. I've been told that it flies fine right up to Mach 1, and the only reason Mmo is .92 is because the FAA requires a .08 cushion between Mmo and Mach 1.

MITaero: well, the book doesn't say how it pulled out, but it does not mention that it was destroyed either, so I presume it pulled out okay. The DC-8 was certified in 1959., and the -40 appeared a year or so later I think, and since this happened in 1961, it could have been a part of some test programme. Probably someone, somewhere was interested what would happen when a subsonic airliner broke the speed of speed of sound. Those was the early years of jets and not much data on that was available I suppose.

I'm pretty sure that the test pilots at Boeing or Airbus commercial divisions do not just run the plane up through the number to see what it will do. After all, there are no ejection seats, even in prototype aircraft. Just how brave do you think these guys are? And if Bill Allen made it very clear to Tex Johnston that he'd just done the last-ever roll in a Boeing 707, what do you think the board of directors would say about taking them supersonic and the risk of bad publicity if it breaks apart?

No, we can be pretty sure that the engineers will define an envelope for the plane and the test pilots will explore that envelope in very methodical fashion.

Then the envelope gets shrunk down to match us ordinary pilots in the form of "Limitations" in the AFM.

The DC-8 going supersonic was very carefully worked out beforehand. The whole story of it is up on the web somewhere. You can probably find a link to it by searching hear regarding "DC-8" and "supersonic." It was not just some cowboy saying "watch this."

Happiness is not seeing another trite Ste. Maarten photo all week long.

The Citation X did indeed first exceed Mach 1 on September 26, 2004. The prototype aircraft (N750CX) was flying with the chase plane, a T-38 (N638TC) owned by Chuck Thornton.

Cessna has an Executive conference room named "Mach 1", which displays a picture of both aircraft. This conference room is near my office.
The Citation X Mmo is 0.92. The margin above Mmo is 0.07, therefore Md is Mach 0.99, which had to be demonstrated for certification, flutter clearance, etc.

"After climbing to an altitude of 52,090 feet, the DC-8-42 series aircraft attained a maximum speed of Mach 1.012 or 660 mph while in a controlled dive through 41,088 feet. The purpose of the flight was to collect data on a new leading-edge design for the wing."

Airliners certified under FAA FAR 25 have a designated Maximum Operating Mach number (Mmo) that can be found on their Type Certificate Data Sheets (see: http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet). This varies from M=.73 (the BAE 146) to M=.92 (the Boeing 747). Beyond this, there is a Dive Mach number (Md). The airliner, in certification, has to be safely taken to this speed (FAR 25.251b). Before roughly 1990, Md was at a minimum Mmo+.05 and Md is now at a minimum Mmo+.07 (FAR 25.335b). This is the speed that an airliner is likely to achieve in an upset maneuver. Some airliners have Md speeds greater than that called for in the regulations. As far as I know, only the Boeing 767 has its dive speed listed on its Type Certificate. The rest are manufacturer's proprietary data.

Md is the highest speed that the airliner has been demonstrated to safely achieve. They can go faster, but this has not been demonstrated to be safe.

Exceeding M1.0 has nothing to do with a dive, if you dive you reduce altitude, so you have temperature increase, and a greater speed of sound, as a(kt)=39vT(°K)
it is when you will cross the conjunction altitude, around FL 240/260 for many jets that, you'll meet max VMO and destroy your aircraft.
if you fly over M1.0 above this altitude, all that can happened is buffeting, then high speed stall and usually spin.
as shown by the DC8 test flights they had to fly over the certified altitudes and moreover the tropopause altitude where temperature is constant to be able to fly above M1.0

25 777236ER
: Not to nitpick, but at that altitude, assuming standard temperature I'd make Mach 1.012 to be 641.24mph, not 660. Uh, above the tropopause at 10km, th

26 777236ER
: Exceeding M1.0 has nothing to do with a dive, if you dive you reduce altitude, so you have temperature increase, and a greater speed of sound, as a(kt

27 Broke
: The large frontal area of today's high by-pass turbofan engines makes it extremely difficult for them to exceed M 1. Even the EgyptAir 767 that went d

28 SlamClick
: "Standard atmosphere" would have the trop height at about 36200' (not 10KM) and the temperature approximately -57.4oC or 214.6oK above that. I have Do

29 SlamClick
: The rationale behind a dive to accelerate through M1 would be just that - trading altitude for speed that the engine thrust might not be able to deliv

30 Speedracer1407
: Regarding the analogy of testing a car under water, I think the point has been missed...at least with this specific analogy. Car manufacturers routine

31 Raivavae
: wrong, you can not compare cars and aircrafts, as the first one are tested on their mechanical resistance, the others is physical, there is nothing to

32 777236ER
: "Standard atmosphere" would have the trop height at about 36200' (not 10KM) and the temperature approximately -57.4oC or 214.6oK above that. I have Do

33 Bellerophon
: Raivavae …Exceeding M1.0 has nothing to do with a dive, if you dive you reduce altitude, so you have temperature increase… Not correct. Above the

34 Raivavae
: I do not agree with you, A dive will increase your Tas by 0.2kt/second for each 1% slope. Diving more than 5°=8% would reduce your speed by increasin

35 777236ER
: A dive will increase your Tas by 0.2kt/second for each 1% slope. Assuming thrust equaling drag, and lift equaling weight, I get the acceleration due t

36 SlamClick
: I guess the real point here is this: There is no point in designing an airplane to go above mach one unless it goes well above mach one. So we had Con

37 Bellerophon
: Raivavae …I do not agree with you… That is your privilege, but, with respect, you are still wrong. ...Diving more than 5°=8% would reduce your sp

38 Raivavae
: Bellerophon, calculations of 777236ER are wrong, as he says 1%slope=0.9°!!!! 1%=0.6° and he is making calculations with only 1% slope dive, I am tal

39 777236ER
: calculations of 777236ER are wrong, as he says 1%slope=0.9°!!!! 1%=0.6° How do you work that out? A 100% slope is 90 degrees, a 50% slope is 45 degr

40 Raivavae
: as you an read in the DC8 article above M1.0 it took 11.000ft above the tropopause to reach this speed, it's not so easy to accelerate above M1.0

41 777236ER
: It was in a 'controlled dive', which could mean they reduced thrust, or added drag using spoilers etc. The numbers seem to imply it's pretty easy.

42 Raivavae
: reducing thrust an exceeding M1.0??!!!! I am sorry to ask what is your occupation? Slopes have nothing to do with mathematics, but with geometry, espe

43 SlamClick
: A 50% slope is not 45o The way to calculate slope in percent is RISE over RUN. That is, for a 50% slope, every hundred feet of linear (not horizontal)

44 777236ER
: reducing thrust an exceeding M1.0??!!!! I am sorry to ask what is your occupation? Listen, simply because I made one mistake, as opposed to the whole

45 Raivavae
: Shall I answer ? Asking for your occupation was not an insult to me, sorry for that, I was just wondering who could say 1%=0.9° lets say you were tir

46 777236ER
: I was just wondering who could say 1%=0.9° lets say you were tired. No, I simply made a mistake. Considering you haven't explained where any of your

47 Raivavae
: my numbers comes from my personal knowledges, that come from MERMOZ school in Paris and the "Guide pratique du Pilote de Ligne", that every french com

48 777236ER
: You don't seem to appreciate that the temperature is constant above 36000ft, and here... Dive more than 5° will significantly increase drag, try in y

49 Raivavae
: I fully agree with the fact that temperature is constant above 36000ft, but airliners are flying rarely above FL380, they usually fly from FL300 to FL

50 777236ER
: Even with my error, and adding 20% for luck, from a cruise of 550kt TAS at 40,000ft, given a 1 degree descent and no change of thrust, you should be g

51 Raivavae
: Airliners are NOT cruising at 550kt at 40000ft, but around 450/500kt at 30000/36000ft. Try the effects of drag with your hand when driving your car, y

52 Vikkyvik
: Raivavae, You're confusing one thing with another. In a dive (or climb), the angle of attack of the wing isn't necessarily any different from it's ang

53 Raivavae
: this is exactly what I wrote, You should read me twice before answering, I said that the angle of attack is about the same, but not only speed increas

54 777236ER
: I said that the angle of attack is about the same, but not only speed increases drag, also the shape of the surface facing the relative wind, and when

55 Raivavae
: so what is incidence for? if you say that it's always the same whatever you are cruising or climbing or diving, when does it change????? You have not

56 777236ER
: Ok, simple test. Take the ATR you claim to fly, set it up in cruise then pitch down 1 degree, while maintaining the same power. Does it accelerate? Pi

57 Raivavae
: max Mmo of ATR is 0.55!!! sure it accelerates at 1° pitch down with no power reduction but anyway we are flying under conjunction altitude, so I will

58 Raivavae
: at 5° it still accelerates (with no power reduction)as it the normal descent path. but with more pith, as in an emergency descent, vertical will be s